The pain associated with the insertion of needles or cannulas into the subcutaneous space is well known and can be addressed in a limited fashion by rubbing anesthetic cream into the insertion site prior to introduction of the rigid cannula (needle) or flexible cannula. Additionally, some drugs incite a stinging sensation, inflammatory response, vaso-dilatory response or pain response during injection for at least some of the duration of the injection or infusion.
Examples of drugs whose infusion causes pain at the infusion-site are adalimumab (Abbott Laboratories, Ill., USA) and treprostinil (United Therapeutics Corp., Md., USA). There are three main methods known in the art for reducing pain at the infusion-site during an injection or infusion:
(1) Preparation of the skin directly prior to the injection, whether by using an anesthetic cream, patch or topical spray containing lidocaine, for example LidoCream 4 (Golden Touch LLC, Ky., USA). The last named is a cream which is typically rubbed into the skin before application of the infusion set.(2) Preparation of the infusion site well in advance of the injection, in order to prepare and numb the area. For example, the use of capsaicin-based patches, such as the Qutenza patch (NeurogesX, Inc., CA, USA) has been shown to have a long term effect which increases towards an optimal level over a couple of weeks.(3) Release of an anesthetic such as lidocaine or bupivacaine from the adhesive layer of an infusion set or patch-pump, as described in US patent application #20110313391.In approaches (1) and (3), the release of the anesthetic is typically only effective for a few hours, after which time the effect gradually drops off. Thus, when infusing a pain-causing drug for periods significantly longer that this, there is a lack of suitable systems to ensure the continuity or refreshing of the pain-relieving effect.